1. Field of the Invention
This patent specification relates to Chromatography. More particularly, this patent specification relates to systems and methods for gas chromatography.
2. Background of the Invention
Chromatography is the field of separating chemicals based on differences in properties such as volatility, absorption, adsorption, size, etc. In this field, different rates of migration along a given flow path (gas, liquid, supercritical fluid, etc) result in the spatial separation of chemical analytes. This differential migration is achieved by differing rates of interaction with the separation column or by different values of analyte mobility. FIG. 1 shows the configuration of a typical conventional gas chromatography system. As shown the configuration includes a pressure source 100, injector 102, a column 104, a detector 106 and vent 108. The injector 102 provides a sharp pulse of the sample (chemical mixture) into the system flow path. The column 104 provides the physical separation, and the detector detects analytes as they elute from the column. Some configurations employ other elements such as a focuser 110, modulator 112, and an additional column 114 to enhance performance or provide otherwise unattainable separations.
Modern chromatography has evolved substantially; many examples exist of advanced methods with various non-standard devices that perform a variety of tasks that provide enhanced chromatographic performance and/or analyte information, as well as hyphenated methods that bridge existing standards and protocols. Such devices include cryogenic focusers, adsorbent based preconcentrators, and band enhancement devices (similar to a focuser). Adding to this complexity are two-dimensional methods that use modulators to control injection into second columns in attempt to measure a second, independent retention time. Also of great significance is the integration of microfabricated devices and systems with traditional chromatographic systems. Microfluidics offer many advantages, but also have the potential for adding new sources of band broadening and other analytical errors. A growing problem common to these relatively recent methods and devices is how to diagnose problems within the system. To achieve the best separation performance, it is necessary to provide injections that are small with respect to the band broadening that will occur on the column. However, with the expected day to day changes in system elements, such as the devices mentioned above, the injection profile could easily change.
Quantitative analysis is typically based on comparison of the observed peak areas to the injected quantity of sample. This can result in a significant error if the sample volume varies (e.g. syringe error) or some injected components do not actually flow from the injector to the column (or between succeeding devices in the flow path).
U.S. Patent Application Publication No. US2005/0123452A1 discloses a chromatograph for analyzing natural gas having non-destructive detectors placed between columns in a multi-column combination. However, these detectors are used for detecting elutes from earlier columns that are discharged prior to a later column having a molecular sieve, so as not to contaminate the sieve. The detectors are not used for diagnosis of problems within the system. A detector is also disclosed in location before the first column. However, this detector is only used during a back-flushing operation where the detector can then detect eluents from the first column.